This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. Bacteriophage P22, one of the best studied Salmonella phages, has been the object of tremendous genetic studies for molecular biology in the past several decades and is remarkable for its converting and transducting abilities. During the virus maturation into the mature phage, it starts as a precursor, called procapsid, with scaffolding proteins inside, then the dsDNA inserts into the expanding capsid shell via one of the twelve vertices, and scaffold proteins exit. The tail attaches to this vertex to become mature and infectious. Although both structures of P22 procapsid and mature phage had been solved to subnanometer (~9 [unreadable] ) resolution by cryo-EM since 2003 (Jiang W. et. al., Nat Struct Biol, 2003, 10:131-5.), most of structural details still remain elusive due to the low resolution.